The role of circulating glucose and fatty acid levels on the rate of lactate production were investigated as well as on other metabolites in the isolated perfused rat lung. Lungs wereperfused with a medium of low glucose, high glucose, low palmitate and high palmitate levels. Lactate production progressively increased withelevated glucose levels with the increase being proportionately higher with Hyperglycemia. Lactate production was unchanged with elevated palmitate in the circulating medium. Pyruvate was significantly (P is less than .05) decreased by hypoglycemia and hypolipopenea. Glucose incorporation into lung lipids was strongly influenced by circulating glucose levels, while palmitate incorporation into lung lipids was markedly influenced by circulating palmitate levels.